Low-energy calibration of XENON1T with an internal $$^{{\textbf {37}}}$$Ar source
E. Aprile, K. Abe, F. Agostini, S. Ahmed Maouloud, M. Alfonsi, L. Althueser, B. Andrieu, E. Angelino, J. R. Angevaare, V. C. Antochi, D. Antón Martin, F. Arneodo, L. Baudis, A. L. Baxter, L. Bellagamba, R. Biondi, A. Bismark, A. Brown, S. Bruenner, G. Bruno, R. Budnik, T. K. Bui, C. Cai, C. Capelli, J. M. R. Cardoso, D. Cichon, A. P. Colijn, J. Conrad, J. J. Cuenca-García, J. P. Cussonneau, V. D’Andrea, M. P. Decowski, P. Di Gangi, S. Di Pede, S. Diglio, K. Eitel, A. Elykov, S. Farrell, A. D. Ferella, C. Ferrari, H. Fischer, W. Fulgione, P. Gaemers, R. Gaior, A. Gallo Rosso, M. Galloway, F. Gao, R. Glade-Beucke, L. Grandi, J. Grigat, M. Guida, R. Hammann, A. Higuera, C. Hils, L. Hoetzsch, J. Howlett, M. Iacovacci, Y. Itow, J. Jakob, F. Joerg, A. Joy, N. Kato, M. Kara, P. Kavrigin, S. Kazama, M. Kobayashi, G. Koltman, A. Kopec, F. Kuger, H. Landsman, R. F. Lang, L. Levinson, I. Li, S. Li, S. Liang, S. Lindemann, M. Lindner, K. Liu, J. Loizeau, F. Lombardi, J. Long, J. A. M. Lopes, Y. Ma, C. Macolino, J. Mahlstedt, A. Mancuso, L. Manenti, F. Marignetti, T. Marrodán Undagoitia, K. Martens, J. Masbou, D. Masson, E. Masson, S. Mastroianni, M. Messina, K. Miuchi, K. Mizukoshi, A. Molinario, S. Moriyama, K. Morå
Abstract
Abstract A low-energy electronic recoil calibration of XENON1T, a dual-phase xenon time projection chamber, with an internal $${}^{37}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>37</mml:mn> </mml:msup> </mml:math> Ar source was performed. This calibration source features a 35-day half-life and provides two mono-energetic lines at 2.82 keV and 0.27 keV. The photon yield and electron yield at 2.82 keV are measured to be ( $$32.3\,\pm \,0.3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>32.3</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>0.3</mml:mn> </mml:mrow> </mml:math> ) photons/keV and ( $$40.6\,\pm \,0.5$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>40.6</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:math> ) electrons/keV, respectively, in agreement with other measurements and with NEST predictions. The electron yield at 0.27 keV is also measured and it is ( $$68.0^{+6.3}_{-3.7}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>68</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mn>0</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>3.7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>6.3</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> ) electrons/keV. The $${}^{37}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>37</mml:mn> </mml:msup> </mml:math> Ar calibration confirms that the detector is well-understood in the energy region close to the detection threshold, with the 2.82 keV line reconstructed at ( $$2.83\,\pm \,0.02$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>2.83</mml:mn> <mml:mspace/> <mml:mo>±</mml:mo> <mml:mspace/> <mml:mn>0.02</mml:mn> </mml:mrow> </mml:math> ) keV, which further validates the model used to interpret the low-energy electronic recoil excess previously reported by XENON1T. The ability to efficiently remove argon with cryogenic distillation after the calibration proves that $${}^{37}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>37</mml:mn> </mml:msup> </mml:math> Ar can be considered as a regular calibration source for multi-tonne xenon detectors.